A hydraulic composition is generally composed of a hydraulic substance such as cement, an aggregate such as fine or coarse aggregate, and water. Since it is a collection of inorganic materials having different specific gravity, particle shape and particle size, it is essentially liable to material separation or segregation. The hydraulic composition having undergone segregation suffers from the serious problem that the composition as hardened varies in quality, or varies or lowers in strength. The segregation may be inhibited by increasing the viscosity of the hydraulic composition to prevent inorganic materials from settling down.
For increasing the viscosity of the hydraulic composition, it would be effective to add water-soluble polymer as the viscosity increasing agent or thickener. Usually cement is strongly alkaline as demonstrated by a pH value of 12 or higher because many Ca2+ ions are available from calcium oxide which is one component of cement. Since the water-soluble polymer is thus exposed to rigorous conditions including decomposition by alkali and agglomeration by metal ions, most water-soluble polymers fail to increase the viscosity of the system. Cellulose ethers, nonionic water-soluble polymers are a few water-soluble polymers that can increase the viscosity of the system.
Water-soluble cellulose ethers such as hydroxypropyl methyl cellulose, which are water-soluble polymers, are effective for increasing viscosity even in concrete. They are widely used in concrete applications including antiwashout underwater concrete (for inhibiting separation during under-water application), spraying concrete (for preventing dust generation during spraying), and self-consolidating concrete (for inhibiting material separation).
Also, diutan gum and welan gum which are water-soluble polymers are used in hydraulic compositions such as mortar and concrete. For example, JP-A 2011-509908 discloses the use of diutan gum in highly self-consolidating concrete.
However, since water-soluble cellulose ether is generally used in powder form, it is awkward to handle as compared with other admixtures which are liquid. The cellulose ether tends to form clumps when added. When a minor amount of cellulose ether is added, scattering makes it difficult to add a desired amount.
To solve the problem, a one-component water-reducing agent obtained by previously combining water-soluble cellulose ether with a water-reducing agent is proposed. For example, JP-A 2008-137889 discloses a combination of a defoamer with water-soluble cellulose ether and a water-reducing agent.